[TowerTalk] 1 or 2 dB

Tue May 24 16:16:17 EDT 2022

That is a reasonable point, Stan. That is why I was suggesting that it 
would be instructive to use logs where output power wasn't varied as 
experimental controls. You could slice a "control" log up in multiple 
ways to see how much difference the length of the slicing interval would 
make. It could be that slicing into 10 minute slots instead 1 minutes 
slots still produces nearly equal score outcomes when comparing odd slot 
and even slots scores on a control log where power was held constant.

Your comments speak to another aspect of the 1dB measurement which is 
context. As you point out, being loud during a feeding frenzy of Euros 
chasing a Caribbean station during a strong opening can actually be a 
disadvantage. OTOH, when the band is barely open to JA/BY/BU/VR2/JT on 
160 or 80 meters, the 1dB could be the difference between getting over 
the noise floor of a double mult and not. So at the end of the day, if 
you ran the proposed experiment, you might find that 1dB does make a 
certain percentage difference in score. The problem is that particular 
measured difference is going to represent the average advantage over the 
particular set of conditions presented by that particular contest with 
the chosen length of the time slice interval. Under a different set of 
particular conditions presented by a different contest, geographical 
location, operator, solar conditions and/or slicing interval, the 
measured advantage of 1dB could vary considerably.

BTW, I agree that it makes intuitive sense that every dB helps, 
otherwise low power scores would not be on average significantly lower 
than high power scores. However, how one extrapolates from the clear 
advantage of an ~10dB increase to the advantage of a 1dB increase seems 
a little unclear to me. If you assume that every 1dB increase in power 
yields the same amount of score improvement no matter where you are on 
continuum from attic dipole to multi-tower superstation, then the 
benefit of 1dB should be equal to:

     Benefit_1dB = Benefit_10dB^(1/10).

So if by comparing high power and low power scores, the average score 
benefit of the 10dB advantage is found to be 40%, then the average 
benefit of 1dB could be assumed to be 1.4^(1/10) = 1.03457 (i.e. 
3.457%). Again, however, that calculation has the assumption baked into 
it that all 1dB power increases yield the same score benefit no matter 
what the size of your station.

Anyway, I've beat this deceased beast enough already, so I'll shut up.

73, Mike W4EF...

On 5/20/2022 3:56 PM, Stan Stockton wrote:
> A couple years ago I reduced power from 1200w to 50 watts to thin a gigantic pileup of Europeans on 160.  Rate went way up after about five minutes.  I think even without that situation occurring you would have to increase the times for each power to 10 minutes or more to see the impact.  Every other minute won’t tell you anything in my opinion.  Those who have gone to great effort to gain another dB or so over what they had know, intuitively, that it makes a significant difference.
>
> Stan, K5GO/ZF9CW
>
> Sent from my iPhone
>
>> On May 20, 2022, at 5:43 PM, Michael Tope <W4EF at dellroy.com> wrote:
>> If you use a differencing method that inserts and removes the 1dB transmit attenuator in a way that is not known to the operator and that ensures the operators spends an equal amount of time at each power level, then the impact of the 1dB "psych out" would presumably get spread equally between the two power levels. The key is engineering the attenuator control so that the system doesn't give off subtle clues that it has changed state (e.g. change in VSWR, change in plate or drain current, sound of vacuum relays clicking, etc). Of course, as N5OP suggests, getting volunteers who are representative (i.e. highly competitive individuals) who are willing to subject themselves to being at a small power disadvantage 50% of the time, might be a challenge. 😉
>>
>> 73, Mike W4EF....................
>>
>> On 5/19/2022 4:24 PM, David Hachadorian wrote:
>>> Just knowing that you are wasting 21% of your output power in an unnecessary 1 dB of feed line loss will play with your head and cause you to perform sub-optimally.
>>>
>>> Dave Hachadorian, K6LL
>>> Yuma, AZ
>>>
>>>
>>> On 5/19/2022 3:01 PM, Lux, Jim wrote:
>>>> On 5/19/22 11:38 AM, Jim Brown wrote:
>>>>> On 5/19/2022 6:23 AM, Lux, Jim wrote:
>>>>>> I'm not so sure that it's out of reach. yes, trying to implement it with gear from 1980 would be challenging. But with more modern equipment, where the "radio" is a black box controlled by a "front panel" or "computer" it gets easier.
>>>>> The Elecraft K3 with second RX that is the same as the main RX, and which can be synced with the main, allows diversity reception, and I've been using it since 2008.
>>>>> Diversity requires an antenna for each RX, spaced as widely as practical from each other. It was invented in the earliest days of radio to counter the effect of selective fading, which is the the cancellation of two or more arrivals of the wavefront from the same TX that have followed different paths, arriving at different times. The time differences cause the arrivals to have a variable phase relationship with each other, combining algebraically to cancel or add, depending on the resulting phase relationships. Diversity works best when the antennas have the greatest spacing, so that when cancellation is occurring at one antenna, it is less likely to do so, or even to increase, at the other.
>>>>>> And the diversity combining - doing it in analog is hard, but in the digital domain it's much easier, and for the most part it can be done at audio (or post down conversion to baseband or low IF).
>>>>> As diversity has been practiced since the beginning, combination is done in the brain of the operator, with audio from the two receivers in opposing ears. That's how it's done in the K3. The result is a sort of spatiality to the sound, a bit like the true stereo image produced by a spaced pair of microphones dedicated to left and right loudspeakers.
>>>>> Combining the outputs of the two receivers to a single (mono) channel is problematic, because the phase relationships at audio have a good chance of cancelling.
>>>> For SSB, yes - a simple summing won't work.  But it's widely used in other systems where there's some processing or where the baseband phase is reliable  - For instance, on AM or FM, the instantaneous audio phase will match, so you coherently combine - typically modern diversity receive does some sort of weighting on the basis of SNR - the stronger signal gets a heavier weight, and when there's fading, it smoothly changes.
>>>> I will say that there are *bad* implementations - I had a car radio that did diversity on FM, but the two paths were noticeably different time delay (as in milliseconds) so you could hear an apparent "echo" as it switched from one to the other.
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